Solid state imager dies, such as a CMOS imager die, typically contain thousands of pixel cells in a pixel cell array on a single chip. Pixel cells convert radiant energy into an electrical signal that can then be stored and recalled by an electrical device such as, for example, a processor. The electrical signals that are stored may be recalled to produce an image on, for example, a computer screen or a printable media.
Exemplary CMOS imaging circuits, processing steps thereof, and detailed descriptions of the functions of various CMOS elements of an imaging circuit are described, for example, in U.S. Pat. Nos. 6,140,630; 6,376,868; 6,310,366; 6,326,652; 6,204,524; 6,333,205 each of which being assigned to Micron Technology, Inc. The disclosures of each of the forgoing patents are hereby incorporated by reference in their entirety.
FIG. 1 illustrates a block diagram of a conventional integrated circuit 10. The integrated circuit includes a die 12 having an imager device 8 included thereon; as illustrated and for exemplary discussions, the imager device is a CMOS device 8. The imager device 8 has a pixel cell array 14 that comprises a plurality of pixel cells arranged in a predetermined number of columns and rows. The pixel cells of each row in the pixel cell array 14 are all turned on at the same time by a row select line, and the pixel cells of each column are selectively output by respective column select lines. A plurality of row and column lines are provided for the entire pixel cell array 14. The row lines are selectively activated in sequence by a row driver 1 in response to row address decoder 2 and the column select lines are selectively activated in sequence for each row activation by a column driver 3 in response to column address decoder 4. The imager device 8 is operated by the control circuit 5, which controls address decoders 2, 4 for selecting the appropriate row and column lines for pixel cell readout, and row and column driver circuitry 1, 3 to apply driving voltage to the drive transistors of the selected row and column lines.
The pixel cell output signals typically include a pixel reset signal Vrst taken from a charge storage node when it is reset and a pixel image signal Vsig, which is taken from the storage node after charges generated by an image are transferred to the node. The Vrst and Vsig signals are read by a sample and hold circuit 6 and are subtracted by a differential amplifier 7, which produces a difference signal (Vrst−Vsig) for each pixel cell, which represents the amount of radiant energy impinging on the pixel cell. The signal difference is digitized by an analog-to-digital converter 9. The digitized signal difference is then fed to an image processor 11 to form and output a digital image. In addition, as depicted in FIG. 1, the imager device 8 components may all be included on a single die 12 to form the integrated circuit 10 or the components may be integrated on a plurality of dies. The integrated circuit(s) 10 can be included in a number of image capture and/or reproduction applications, including, but not limited to, sensors, cameras, personal digital assistants (PDAs), scanners, facsimile machines, and copiers.
Radiant energy directed towards the pixel cell array 14 during image capture also strikes the peripheral circuitry of the imager device 8, which can interfere with proper image capture. For example, radiant energy could strike the circuitry, e.g., transistors and capacitors (not shown), of the row driver 1, decoders 2, 4, analog-to-digital converter 9, image processor 11, timing and control circuit 5, and/or the column driver 3. The peripheral circuitry typically comprises transistors, capacitors, and other components that are susceptible to noise when exposed to varying amounts of radiant energy. This can lead to image artifacts, such as column-banding, significantly degrading imager device performance.
Accordingly, there is a desire and need for a solid state imager device that has eliminated or reduced the amount of radiant energy striking the peripheral circuitry of the imager device, thereby decreasing the amount of noise in the image, and leading to better image quality.